An embodiment of the present invention relates generally to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a superjunction device by ion implanting trenches using four different implantation directions that are generally non-orthogonal to the orientations of the trenches.
Since the invention of superjunction devices by Dr. Xingbi Chen, as disclosed in U.S. Pat. No. 5,216,275, the contents of which are incorporated by reference herein, there have been many attempts to expand and improve on the superjunction effect of his invention. U.S. Pat. Nos. 6,410,958, 6,300,171 and 6,307,246 are examples of such efforts and are incorporated by reference herein.
Trench type superjunction devices are expected to replace multi-epi superjunction devices because of the potential lower processing cost. FIG. 1A illustrates a top plan view of a wafer 10 used in manufacturing of a plurality of trench-type superjunction devices. A plurality of horizontally oriented trenches 12 are formed therein. FIGS. 1B and 1C are enlarged partial cross-sectional views of the wafer 10 both taken along the line A-A′. In general, a superjunction device is produced through formation of n or p columns (not shown) using adjacent sidewalls 14, 16 of the trenches 12. Doping with a dopant of n-type or p-type conductivity is performed by ion implantation at an appropriate tilt angle Φ (or φ′ in FIG. 1C). The dopant impurities are thereby generally uniformly implanted at the tilt angles Φ, Φ′ throughout the sidewalls 14, 16 of each of the trenches 12.
Implantation is typically performed at a direction having a rotation angle θ that is generally orthogonal to the orientation of the trench 12. For example, in FIG. 1A, the trenches 12 have a horizontal orientation, and a first implantation direction 21 is shown in a vertical orientation, in the plane of the wafer 10, for implanting the first sidewalls 14 of the trenches 12 (see FIG. 1B). A second implantation direction 22 is also shown in a vertical orientation, opposite to the first implantation direction 21, for implanting the second sidewalls 16 of the trenches 12 (see FIG. 1C).
In certain applications, a semiconductor wafer will include two or more sets of trenches having different orientations. For example, FIG. 2 shows a wafer 11 including one set of trenches 12 having a horizontal orientation (as in FIG. 1A) and a second set of trenches 13 having a vertical orientation. For wafer 11, four implantation directions are required in order to properly dope all of the sidewalls (not shown) of all of the trenches 12, 13. For example, implantation directions 21, 22, orthogonal to the trenches 12, are used for implanting the dopant into the sidewalls of the trenches 12. Likewise, implantation directions 23, 24, orthogonal to the trenches 13, are used for implanting the sidewalls of the trenches 13.
The four angle implantation method described above is satisfactory for wafers having trenches or trench sets orthogonally aligned with one another, and the trenches each having identical doping concentrations. However, difficulties arise when the trenches are not orthogonal to one another or in situations where differing doping concentrations are required. The ion dose and/or the acceleration energy of the ion beam must be changed during processing or multiple implantation steps may be required, which increases the complexity, cost, and time for manufacturing the superjunction devices.
It is desirable to provide a method of manufacturing trench-type superjunction devices having trenches non-orthogonally aligned to one another without having to change the orientation or the ion beam strength mid-step or perform additional implantation steps. It is further desirable to provide a method of manufacturing superjunction devices wherein varying doping concentrations of different trenches may be achieved simultaneously.